This invention relates to electric heating coils as used in cigar lighters, ignitor plugs and the like, and more particularly to a production method and apparatus by which spiral heating coils (which can if desired have nestable convolutions) are produced.
For many years the heating coils of electric cigar lighters as used in automobiles were wound of flat, ribbon-like resistance wire into a spiral coil shape, utilizing an arbor and related fixtures, in a relatively slow speed process involving appreciable hand labor and handling. As so produced, the heating elements were somewhat costly and in many cases lacked uniformity, being not of especially high quality, since rigid standards were not usually required. Such heating elements were utilized with 6-volt electrical systems of automobiles, for the most part. When automobile electrical systems were improved by changing to 12-volt batteries it became necessary to use a greater length of thinner resistance-wire ribbon in the cigar lighters so as to accommodate these to the higher voltage. In so doing, the spiral-wound heating elements were found to be much less sturdy and rugged, and many instances occured where the coil convolutions become deformed or short-circuited, causing a safety hazard in addition to rendering the cigar lighter inoperative.
In order to remedy this condition, spiral-wound heating coils were experimented with and produced where a ribbed or angular cross-sectional configuration was imparted to the ribbon, so as to cause nesting of adjoining convolutions of the spiral coil whereby greater rigidity and mutual support were had. This resulted in an improved, sturdier and more rugged coil, and eliminated to a great extent the prior coil failures and burn-outs. The ribbing of the ribbon was done by placing cut lengths in a flat die of a press, and applying a punch to the ribbon to form the groove-like configuration. This particular procedure was not only lengthy and costly, but it also produced a high percentage of rejects. Thus, while a solution to one problem was had, there arose other problems which tended to detract from the advantages of ribbing the ribbon. For example, the use of thinner ribbon resulted in coils being more unwieldly, and greater care was required in performing the spiral winding. Due to the hand operations which were involved, regardless of whether or not the ribbon was ribbed, the labor cost remained high. In addition, there was lacking the uniformity and high quality which generally characterizes parts or components that are accurately made mostly by machine operations capable of being closely controlled.